Firefighters at the scene of an explosion and building collapse in East Harlem on Wednesday, March 12, 2014. Photo Credit: Jim Slevin @ufanyc

Pianos were launched into the air when a "huge boom" rocked the East Harlem piano store where Colin Patterson works.

"The pianos flew off the ground and flew around me," said Patterson, a piano technician at Absolute Piano on the ground floor at 1646 Park Ave., one of two buildings leveled Wednesday morning by a massive explosion caused by a suspected gas leak.

Patterson, finding himself "in a miraculous cocoon" of debris after the blast, managed to dig himself out and crawl through a window, escaping with only a scratch on his left wrist.

"It was a huge boom, like a sonic jet engine. The building fell on top of me," said Patterson, who has lived on the building's ground floor for 10 years.

The 9:30 a.m. explosion, powerful enough for witnesses to mistake for an earthquake, could be heard across a large swath of upper Manhattan.

As the buildings crumbled, shards of glass and tons of bricks rained down on the busy street below. Parked cars were crushed, and railroad tracks nearby were covered with debris, shutting down rail service.

Casareo and co-worker Alex Camillo, 35, of Manhattan, also rescued two people from a minivan that had been partly crushed by falling debris.

"We pulled the people out of the window," Camillo said.

Gregory Garcia, 50, who has lived in the neighborhood his whole life, said the explosion "sounded like a bomb. My building shook. I felt a vibration through my body."

Carlos Perez, 60, was on the block working at a shop that sells medicinal herbs.

"When I heard the explosion, it broke all the windows and shattered glass onto my chest. I thought it was a train that might have derailed," he said. "I ran out to the corner and there was smoke everywhere."